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Message-ID: <20151209164108.GB3886@mrl.redhat.com>
Date: Wed, 9 Dec 2015 14:41:08 -0200
From: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Vlad Yasevich <vyasevich@...il.com>,
netdev <netdev@...r.kernel.org>,
Eric Dumazet <eric.dumazet@...il.com>,
syzkaller <syzkaller@...glegroups.com>,
linux-sctp@...r.kernel.org, Kostya Serebryany <kcc@...gle.com>,
Alexander Potapenko <glider@...gle.com>,
Sasha Levin <sasha.levin@...cle.com>
Subject: Re: use-after-free in sctp_do_sm
On Wed, Dec 09, 2015 at 01:03:56PM -0200, Marcelo Ricardo Leitner wrote:
> On Wed, Dec 09, 2015 at 03:41:29PM +0100, Dmitry Vyukov wrote:
> > On Tue, Dec 8, 2015 at 8:22 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> > > On Tue, Dec 8, 2015 at 6:40 PM, Marcelo Ricardo Leitner
> > > <marcelo.leitner@...il.com> wrote:
> ...
> > >> The patches were combined already, but this last pick by Vlad is just
> > >> not yet patched. It's not necessary for your testing and I didn't want
> > >> to interrupt it in case you were already testing it.
> > >>
> > >> You can use my last patch here, from 2 emails ago, the one which
> > >> contains this line:
> > >> - case SCTP_DISPOSITION_ABORT:
> > >
> > >
> > > You are right. I missed that they are combined. Testing with it now.
> >
> >
> >
> >
> > Use-after-free still happens.
> > I am on commit aa53685549a2cfb5f175b0c4a20bc9aa1e5a1b85 (Dec 8) plus
> > the following sctp-related changes:
>
> Changes are fine. Ugh. Ok, I'll try your new reproducer here.
Heh I wasn't going to reproduce this by myself anytime soon, I think.
It's using the same socket to connect to itself, and only happens if the
connect() gets there before the listen() call. Figured this out because
I could only reproduce it under strace at first.
Please give this other patch a try. A state command
(sctp_sf_cookie_wait_prm_abort) was issuing SCTP_CMD_INIT_FAILED, which
leads to SCTP_CMD_DELETE_TCB, but returning SCTP_DISPOSITION_CONSUME,
which fooled the patch.
---8<---
commit 9f84d50e36cee0ce66e4ce9b3b1665e0a1dbcdd3
Author: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Date: Fri Dec 4 15:30:23 2015 -0200
sctp: fix use-after-free in pr_debug statement
Dmitry Vyukov reported a use-after-free in the code expanded by the
macro debug_post_sfx, which is caused by the use of the asoc pointer
after it was freed within sctp_side_effect() scope.
This patch fixes it by allowing sctp_side_effect to clear that asoc
pointer when the TCB is freed.
As Vlad explained, we also have to cover the SCTP_DISPOSITION_ABORT case
because it will trigger DELETE_TCB too on that same loop.
Also, there was a place issuing SCTP_CMD_INIT_FAILED but returning
SCTP_DISPOSITION_CONSUME, which would fool the scheme above. Fix it by
returning SCTP_DISPOSITION_ABORT instead.
The macro is already prepared to handle such NULL pointer.
Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
index 6098d4c42fa9..be23d5c2074f 100644
--- a/net/sctp/sm_sideeffect.c
+++ b/net/sctp/sm_sideeffect.c
@@ -63,7 +63,7 @@ static int sctp_cmd_interpreter(sctp_event_t event_type,
static int sctp_side_effects(sctp_event_t event_type, sctp_subtype_t subtype,
sctp_state_t state,
struct sctp_endpoint *ep,
- struct sctp_association *asoc,
+ struct sctp_association **asoc,
void *event_arg,
sctp_disposition_t status,
sctp_cmd_seq_t *commands,
@@ -1123,7 +1123,7 @@ int sctp_do_sm(struct net *net, sctp_event_t event_type, sctp_subtype_t subtype,
debug_post_sfn();
error = sctp_side_effects(event_type, subtype, state,
- ep, asoc, event_arg, status,
+ ep, &asoc, event_arg, status,
&commands, gfp);
debug_post_sfx();
@@ -1136,7 +1136,7 @@ int sctp_do_sm(struct net *net, sctp_event_t event_type, sctp_subtype_t subtype,
static int sctp_side_effects(sctp_event_t event_type, sctp_subtype_t subtype,
sctp_state_t state,
struct sctp_endpoint *ep,
- struct sctp_association *asoc,
+ struct sctp_association **asoc,
void *event_arg,
sctp_disposition_t status,
sctp_cmd_seq_t *commands,
@@ -1151,7 +1151,7 @@ static int sctp_side_effects(sctp_event_t event_type, sctp_subtype_t subtype,
* disposition SCTP_DISPOSITION_CONSUME.
*/
if (0 != (error = sctp_cmd_interpreter(event_type, subtype, state,
- ep, asoc,
+ ep, *asoc,
event_arg, status,
commands, gfp)))
goto bail;
@@ -1174,11 +1174,12 @@ static int sctp_side_effects(sctp_event_t event_type, sctp_subtype_t subtype,
break;
case SCTP_DISPOSITION_DELETE_TCB:
+ case SCTP_DISPOSITION_ABORT:
/* This should now be a command. */
+ *asoc = NULL;
break;
case SCTP_DISPOSITION_CONSUME:
- case SCTP_DISPOSITION_ABORT:
/*
* We should no longer have much work to do here as the
* real work has been done as explicit commands above.
diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index 6f46aa16cb76..d801e151498a 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -4959,12 +4959,10 @@ sctp_disposition_t sctp_sf_cookie_wait_prm_abort(
sctp_cmd_seq_t *commands)
{
struct sctp_chunk *abort = arg;
- sctp_disposition_t retval;
/* Stop T1-init timer */
sctp_add_cmd_sf(commands, SCTP_CMD_TIMER_STOP,
SCTP_TO(SCTP_EVENT_TIMEOUT_T1_INIT));
- retval = SCTP_DISPOSITION_CONSUME;
sctp_add_cmd_sf(commands, SCTP_CMD_REPLY, SCTP_CHUNK(abort));
@@ -4983,7 +4981,7 @@ sctp_disposition_t sctp_sf_cookie_wait_prm_abort(
sctp_add_cmd_sf(commands, SCTP_CMD_INIT_FAILED,
SCTP_PERR(SCTP_ERROR_USER_ABORT));
- return retval;
+ return SCTP_DISPOSITION_ABORT;
}
/*
--
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